Grief is a normal part of adjusting to change. The scale of grief changes depending on the emotional importance of the change to the self. Mostly the grief is mourning loss, whether the loss of an object, a person or an opportunity.
Grief allows the self to change from what was to what is. Without it we are stuck in limbo. Sometimes, though, we become stuck in this adjustment. Instead of a process, we are mired in the pits of grief driven depression. At this point one may need professional help to get the grief process going again.
If we nip this problem in the bud too early, we interrupt the process in another way, not allowing us to adjust to change.
The new version of the Diagnostics and Statistical Manual Five (DSM V), published by the American Psychology Association, seems to defining regular grief as a clinical disorder. If this is so I believe that new professionals may over prescribe medication on yet another common element of life.